1. Field of the Invention
The present invention relates to a video signal processing apparatus, a video signal processing method, and a computer program product, and, more particularly, to a video signal processing apparatus, a video signal processing method, and a computer program product for converting interlaced video signals into progressive video signals.
2. Description of the Related Art
Liquid display devices and organic EL (Electro-Luminescence) display devices display video images by a frame-hold-type display processing, unlike display devices using CRTs (Cathode Ray Tubes). For example, a display device that operates at the regular frame frequency of 60 Hz displays an image in a frame-hold-type display processing, holding one image on the entire screen in every display period in one frame.
Many broadcast signals for displaying video images are generated by the interlace method compatible with display devices using CRTs. When an image is displayed with interlaced broadcast signals on a display device using a CRT, each one image to be displayed on the horizontal scanning lines of the CRT is formed with two fields. In the first field of the two fields, the horizontal scanning lines are scanned every other line from the uppermost horizontal scanning line of the screen. When the scanning reaches the lower-end horizontal scanning line, the horizontal scanning lines that have not been scanned in the first field are scanned every other line from the top of the screen. In this manner, the image of one frame is displayed.
When an image is displayed on a display device that displays an image in a frame-hold-type display processing such as a liquid crystal display device or an organic EL display device using interlaced broadcast signals (hereinafter also referred to simply as “interlaced signals”), a line that carries data to be displayed on the screen and a line that does not carry data alternately appear in each display frame, and many flickers are caused. As a result, the luminance is halved. To counter this issue, an operation to convert interlaced signal into progressive broadcast signals (hereinafter also referred to simply as “progressive signals”) is performed in each display device that displays an image in a frame-hold-type display processing. The operation to convert interlaced signals into progressive signals is generally called an I-P converting operation.
The progressive method is a method for displaying a screen by scanning the scanning lines forming the screen one by one from the top. Accordingly, by the progressive method, the signals corresponding to all the scanning lines are provided in one frame. By the interlace method, the horizontal scanning lines are scanned every other line. Therefore, it is necessary to generate signals for the scanning lines that are not scanned by the interlace method. This is the I-P converting operation.
In a case where it is difficult to use the data from the previous and later fields in an I-P converting operation as the movement is large as in moving pictures, the signals of the scanning lines that are not scanned by the interlace method are generated through an interpolating operation. FIG. 13 schematically shows the interpolating operation involving the I-P conversion. As shown in FIG. 13, the signal of the scanning line that is not scanned is generated by performing the interpolating operation with the use of the signals of the scanning lines located above and below the scanning line that is not scanned.
In recent years, attention is drawn to display devices that display images with liquid crystal displays or projectors, inputting interlaced signals of several screens (for example, two screens in the vertical direction and two screens in the horizontal direction). The interlaced signals used in such display devices can display superfine images, like HD-SDI (High Definition-Serial Digital Interface) signals including signals of 1125 lines in the vertical direction. In such display devices, a superfine image can be displayed on a wide screen by inputting video signals of several screens.